Restrained Shrinkage Tests on Fiber Reinforced Cementitious Composites

The usefulness of fiber reinforcement in improving the cracking resistance of cement-based materials under restrained shrinkage conditions is indisputable. In fact, in many situations, it may be the sole reason for adding fibers to concrete. In spite of this fact, there is no universally accepted technique of demonstrating or quantifying the effectiveness of fibers under the conditions of restrained shrinkage. This paper describes a newly developed technique where prismatic specimens with a linear restraint along the longitudinal axis are subjected to a drying environment such that conditions of uni-axial tension are created. The specimen cracks under these conditions and if fiber reinforcement is present, the influence of fibers on the cracking pattern can be established. Results with seven types of fibers are presented. Based on the observations of the crack patterns, a "fiber efficiency factor" is proposed that appears to be an appropriate basis for characterizing the fibers.